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整数类型一共有 5 种，包括 TINYINT、SMALLINT、MEDIUMINT、INT（INTEGER）和 BIGINT。




整数类型
字节
有符号范围
无符号范围



TINYINT
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                    <h1 class="description center-align post-title">MySQL之常见的数据类型和约束</h1>
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                <h1 id="常见的数据类型和约束"><a href="#常见的数据类型和约束" class="headerlink" title="常见的数据类型和约束"></a>常见的数据类型和约束</h1><h1 id="数据类型"><a href="#数据类型" class="headerlink" title="数据类型"></a>数据类型</h1><h3 id="数值型："><a href="#数值型：" class="headerlink" title="数值型："></a>数值型：</h3><h4 id="整型"><a href="#整型" class="headerlink" title="整型"></a>整型</h4><ul>
<li>整数类型一共有 5 种，包括 <code>TINYINT、SMALLINT、MEDIUMINT、INT（INTEGER）和 BIGINT</code>。</li>
</ul>
<table>
<thead>
<tr>
<th>整数类型</th>
<th>字节</th>
<th>有符号范围</th>
<th>无符号范围</th>
</tr>
</thead>
<tbody><tr>
<td>TINYINT</td>
<td>1</td>
<td>-128 ~ 127</td>
<td>0 ~ 255</td>
</tr>
<tr>
<td>SMALLINT</td>
<td>2</td>
<td>-32768 ~ 32767</td>
<td>0 ~ 65535</td>
</tr>
<tr>
<td>MEDIUMINT</td>
<td>3</td>
<td>-8388608 ~ 8388607</td>
<td>0 ~ 16777215</td>
</tr>
<tr>
<td>INT/INTEGER</td>
<td>4</td>
<td>-2147483648 ~ 2147483647</td>
<td>0 ~ 4294967295</td>
</tr>
<tr>
<td>BIGINT</td>
<td>8</td>
<td>-9223372036854775808 ~ 9223372036854775807</td>
<td>0 ~ 18446744073709551615</td>
</tr>
</tbody></table>
<p>如何设置无符号和有符号</p>
<pre class="line-numbers language-sql" data-language="sql"><code class="language-sql"><span class="token keyword">drop</span> <span class="token keyword">table</span> <span class="token keyword">if</span> <span class="token keyword">exists</span> tab_int<span class="token punctuation">;</span>
<span class="token keyword">create</span> <span class="token keyword">table</span> tab_int{
	t1 <span class="token keyword">int</span>
	t2 <span class="token keyword">int</span> <span class="token keyword">unsigned</span>
}<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span></span></code></pre>

<p>特点：</p>
<p>如果不设置无符号有符号，默认有符号，要设置无符号，追加unsigned关键字</p>
<p>如果插入的数值超出了整型的范围，会报out of range异常，并且插入临界值</p>
<p>如果不设置长度，会有默认长度，长度并不是指实际字符长度，字符长度只有前面的数据类型决定，长度代表了显示的最大宽度，如果不够会用0在左边填充，但必须搭配zerofill使用，并且当使用<code>ZEROFILL</code>时，自动会添加<code>UNSIGNED</code></p>
<h4 id="小数（定点数、浮点数）"><a href="#小数（定点数、浮点数）" class="headerlink" title="小数（定点数、浮点数）"></a>小数（定点数、浮点数）</h4><h5 id="定点数：decimal、"><a href="#定点数：decimal、" class="headerlink" title="定点数：decimal、"></a>定点数：decimal、</h5><h5 id="浮点数：float、double"><a href="#浮点数：float、double" class="headerlink" title="浮点数：float、double"></a>浮点数：float、double</h5><table>
<thead>
<tr>
<th>类型名称</th>
<th>占用字节</th>
<th>存储范围</th>
</tr>
</thead>
<tbody><tr>
<td>float</td>
<td>4</td>
<td>0 和 -1.175494351E-38～-3.402823466E+38</td>
</tr>
<tr>
<td>double</td>
<td>8</td>
<td>0 和 -2.2250738585072014E-308～-1.7976931348623157E+308</td>
</tr>
<tr>
<td>decimal(M, D)或dec(M,D)</td>
<td>M+2 个字节</td>
<td>依赖于M和D的值</td>
</tr>
</tbody></table>
<pre class="line-numbers language-sql" data-language="sql"><code class="language-sql"><span class="token keyword">create</span> <span class="token keyword">table</span> tab_float<span class="token punctuation">(</span>
	f1 <span class="token keyword">float</span><span class="token punctuation">(</span><span class="token number">5</span><span class="token punctuation">,</span><span class="token number">2</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
	f2 <span class="token keyword">double</span><span class="token punctuation">(</span><span class="token number">5</span><span class="token punctuation">,</span><span class="token number">2</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
	f3 <span class="token keyword">decimal</span><span class="token punctuation">(</span><span class="token number">5</span><span class="token punctuation">,</span><span class="token number">2</span><span class="token punctuation">)</span>
<span class="token punctuation">)</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span></span></code></pre>

<p>特点：</p>
<p>①M代表整数+小数位数，D为小数点的位数，</p>
<p>如果超过范围，则插入临界值</p>
<p>②M和D都可以省略,如果是decimal，则M默认为10，D默认为0</p>
<p>如果是float和double，则会随着插入的数值的精度来决定精度</p>
<p>③定点型的精确度较高，如果要求插入的数值的精度较高如货币运算等则考虑使用</p>
<p>原则：</p>
<p>所选择的类型越简单越好，能保存数值的类型越小越好</p>
<h3 id="字符型："><a href="#字符型：" class="headerlink" title="字符型："></a>字符型：</h3><p>较短的文本：char、varchar</p>
<p>较长的文本：text、blob（较长的二进制数据）</p>
<table>
<thead>
<tr>
<th align="center">类型</th>
<th align="center">大小（字符）</th>
<th align="center">用途</th>
</tr>
</thead>
<tbody><tr>
<td align="center">CHAR</td>
<td align="center">0 - 255</td>
<td align="center">定长字符串</td>
</tr>
<tr>
<td align="center">VARCHAR</td>
<td align="center">0 - 65535</td>
<td align="center">变长字符串</td>
</tr>
<tr>
<td align="center">TINYBLOB</td>
<td align="center">0 - 255</td>
<td align="center">不超过 255 个字符的二进制字符串</td>
</tr>
<tr>
<td align="center">TINYTEXT</td>
<td align="center">0 - 255</td>
<td align="center">短文本字符串</td>
</tr>
<tr>
<td align="center">BLOB</td>
<td align="center">0 - 65 535</td>
<td align="center">二进制形式的长文本数据</td>
</tr>
<tr>
<td align="center">TEXT</td>
<td align="center">0 - 65 535</td>
<td align="center">长文本数据</td>
</tr>
<tr>
<td align="center">MEDIUMBLOB</td>
<td align="center">0 - 16 777 215</td>
<td align="center">二进制形式的中等长度文本数据</td>
</tr>
<tr>
<td align="center">MEDIUMTEXT</td>
<td align="center">0 - 16 777 215</td>
<td align="center">中等长度文本数据</td>
</tr>
<tr>
<td align="center">LONGBLOB</td>
<td align="center">0 - 4 294 967 295</td>
<td align="center">二进制形式的极大文本数据</td>
</tr>
<tr>
<td align="center">LONGTEXT</td>
<td align="center">0 - 4 294 967 295</td>
<td align="center">极大文本数据</td>
</tr>
</tbody></table>
<p>补充：</p>
<p>char(M) M:最大字符数，可以省略，默认为1</p>
<p>varchar(M) 最大的字符数，不可以省略</p>
<p>binary和varbinary，类似于char和varchar，不同的是它们包含较短二进制字符串而不包含非二进制字符串。</p>
<p>Enum类型<br>说明：又称为枚举类型哦，要求插入的值必须属于列表中指定的值之一。<br>如果列表成员为1<del>255，则需要1个字节存储<br>如果列表成员为255</del>65535，则需要2个字节存储<br>最多需要65535个成员！</p>
<p>Set类型<br>说明：和Enum类型类似，里面可以保存0~64个成员。和Enum类型最大的区<br>别是：SET类型一次可以选取多个成员，而Enum只能选一个<br>根据成员个数不同，存储所占的字节也不同</p>
<p>成员数        字节数<br>1-8                  1<br>9<del>16              ２<br>17</del>24             3<br>25~32             4<br>33-64              8</p>
<h3 id="日期型"><a href="#日期型" class="headerlink" title="日期型"></a>日期型</h3><p>1、Timestamp支持的时间范围较小，取值范围：<br>19700101080001-—2038年的某个时间<br>Datetime的取值范围：1000-1-1-—9999—12-31<br>timestamp和实际时区有关，更能反映实际的日<br>期，而datetme则只能反映出插入时的当地时区<br>3、timestamp的属性受Mysql版本和SQLMode的影响很大</p>
<p>date只保存日期<br>time只保存时间<br>Year只保存年<br>datetine保存日期+时间<br>timestamp保存日期+时间</p>
<table>
<thead>
<tr>
<th align="left">数据类型</th>
<th align="left">占用字节</th>
<th align="left">最小值</th>
<th align="left">最大值</th>
<th align="left">零值表示</th>
</tr>
</thead>
<tbody><tr>
<td align="left">date</td>
<td align="left">4</td>
<td align="left">1000-01-01</td>
<td align="left">9999-12-31</td>
<td align="left">0000-00-00</td>
</tr>
<tr>
<td align="left">datetime</td>
<td align="left">8</td>
<td align="left">1000-01-01 00:00:00</td>
<td align="left">9999-12-31 23:59:59</td>
<td align="left">0000-00-00 00:00: 00</td>
</tr>
<tr>
<td align="left">timestamp</td>
<td align="left">4</td>
<td align="left">19700101080001</td>
<td align="left">2038年的某个时刻</td>
<td align="left">0000000000000000</td>
</tr>
<tr>
<td align="left">time</td>
<td align="left">3</td>
<td align="left">-838:59:59</td>
<td align="left">838:59:59</td>
<td align="left">00:00:00</td>
</tr>
<tr>
<td align="left">year</td>
<td align="left">1</td>
<td align="left">1901</td>
<td align="left">2155</td>
<td align="left">0000</td>
</tr>
</tbody></table>
<p>注意：datatime不受时区影响，而timestamp受时区影响</p>
<h1 id="常见约束"><a href="#常见约束" class="headerlink" title="常见约束"></a>常见约束</h1><p>用于限制表中的数据，为了保证表中的数据的准确和可靠性</p>
<h2 id="分类：六大约束："><a href="#分类：六大约束：" class="headerlink" title="分类：六大约束："></a>分类：六大约束：</h2><p>​        Not NULL；非空，用于保证该字段的值不能为空</p>
<p>​        Default：默认，保证该字段有默认值</p>
<p>​        Primary：主键：用于保证该字段的值具有唯一性，并且非空</p>
<p>​        Unique：唯一：用于保证该字段的值具有唯一性，可以为空</p>
<p>​        Check：检查约束【mysql中不支持】</p>
<p>​        Foreign Key：外键，用于限制两个表的关系，用于保证该字段的值必须来自于主表关联列的值，在从表添加外键约束，用于引用主表中某列的值</p>
<h2 id="添加约束的时机"><a href="#添加约束的时机" class="headerlink" title="添加约束的时机"></a>添加约束的时机</h2><p>1、创建表时</p>
<p>2、修改表时</p>
<h2 id="约束的添加分类"><a href="#约束的添加分类" class="headerlink" title="约束的添加分类"></a>约束的添加分类</h2><h3 id="列级约束"><a href="#列级约束" class="headerlink" title="列级约束"></a>列级约束</h3><p>六大约束语法上都支持、但外键约束没有效果甚至报错</p>
<pre class="line-numbers language-sql" data-language="sql"><code class="language-sql"><span class="token keyword">create</span> <span class="token keyword">table</span> stuinfo<span class="token punctuation">(</span>
	id <span class="token keyword">int</span> <span class="token keyword">primary</span> <span class="token keyword">key</span><span class="token punctuation">,</span><span class="token comment">#主键</span>
	stuName <span class="token keyword">varchar</span><span class="token punctuation">(</span><span class="token number">20</span><span class="token punctuation">)</span> <span class="token operator">not</span> <span class="token boolean">null</span><span class="token punctuation">,</span><span class="token comment">#非空</span>
	gender <span class="token keyword">char</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span> <span class="token keyword">check</span><span class="token punctuation">(</span>gender<span class="token operator">=</span><span class="token string">'男'</span> <span class="token operator">or</span> gender<span class="token operator">=</span><span class="token string">'女'</span><span class="token punctuation">)</span><span class="token punctuation">,</span><span class="token comment">#检查</span>
	age <span class="token keyword">int</span> <span class="token keyword">default</span> <span class="token number">18</span><span class="token punctuation">,</span><span class="token comment">#默认约束</span>
	majorId <span class="token keyword">int</span> <span class="token keyword">foreign</span> <span class="token keyword">key</span> <span class="token keyword">references</span> major<span class="token punctuation">(</span>id<span class="token punctuation">)</span><span class="token comment">#外键</span>
<span class="token punctuation">)</span>

<span class="token keyword">create</span> <span class="token keyword">table</span> major{
	id <span class="token keyword">int</span> <span class="token keyword">primary</span> <span class="token keyword">key</span><span class="token punctuation">,</span>
	majorName <span class="token keyword">varchar</span><span class="token punctuation">(</span><span class="token number">20</span><span class="token punctuation">)</span>
}<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>



<h3 id="表级约束"><a href="#表级约束" class="headerlink" title="表级约束"></a>表级约束</h3><p>语法：在各个字段的最下面</p>
<p>【constraint 约束名】 约束类型 （字段名）</p>
<p>不起名也有默认名</p>
<p>除了非空、默认，其他都支持</p>
<p>但是正常只有外键作为表级约束</p>
<pre class="line-numbers language-sql" data-language="sql"><code class="language-sql"><span class="token keyword">create</span> <span class="token keyword">table</span> stuinfo<span class="token punctuation">(</span>
	id <span class="token keyword">int</span><span class="token punctuation">,</span><span class="token comment">#主键</span>
	stuName <span class="token keyword">varchar</span><span class="token punctuation">(</span><span class="token number">20</span><span class="token punctuation">)</span><span class="token punctuation">,</span><span class="token comment">#非空</span>
	gender <span class="token keyword">char</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">,</span><span class="token comment">#检查</span>
	seat <span class="token keyword">int</span><span class="token punctuation">,</span><span class="token comment">#唯一</span>
	age <span class="token keyword">int</span><span class="token punctuation">,</span><span class="token comment">#默认约束</span>
	majorId <span class="token keyword">int</span><span class="token punctuation">,</span> <span class="token comment">#外键</span>
	<span class="token keyword">constraint</span> pk <span class="token keyword">primary</span> <span class="token keyword">key</span><span class="token punctuation">(</span>id<span class="token punctuation">)</span><span class="token punctuation">,</span>
	<span class="token keyword">constraint</span> uq <span class="token keyword">unique</span><span class="token punctuation">(</span>seat<span class="token punctuation">)</span><span class="token punctuation">,</span>
	<span class="token keyword">constraint</span> ck <span class="token keyword">check</span><span class="token punctuation">(</span>gender<span class="token operator">=</span><span class="token string">'男'</span> <span class="token operator">or</span> gender<span class="token operator">=</span><span class="token string">'女'</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
	<span class="token keyword">constraint</span> fk_stuinfo_major <span class="token keyword">FOREIGN</span> <span class="token keyword">key</span><span class="token punctuation">(</span>majorid<span class="token punctuation">)</span> <span class="token keyword">REFERENCES</span> major<span class="token punctuation">(</span>id<span class="token punctuation">)</span>
<span class="token punctuation">)</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>

<p>查看表中所有索引，包含主键、外键、唯一</p>
<p>show index from stuinfo;</p>
<pre class="line-numbers language-none"><code class="language-none">Create table 表名{
		字段名 字段类型 列级约束
		字段名 字段类型，
		表级约束
}<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span></span></code></pre>



<p>主键和唯一的对比：</p>
<table>
<thead>
<tr>
<th>类型</th>
<th>保证唯一性</th>
<th>是否允许为空</th>
<th>一个表中可以有多少个</th>
<th>允许组合</th>
</tr>
</thead>
<tbody><tr>
<td>主键</td>
<td>√</td>
<td>×</td>
<td>至多有一个</td>
<td>允许但不推荐</td>
</tr>
<tr>
<td>唯一</td>
<td>√</td>
<td>√</td>
<td>可以有多个</td>
<td>允许但不推荐</td>
</tr>
</tbody></table>
<p>外键特点</p>
<p>1、要求在从表中设置外键关系</p>
<p>2、从表的外键列类型和主表的关联列的类型要求一致或者兼容</p>
<p>3、主表的关联列必须是一个key（一般是主键、唯一）</p>
<p>4、插入数据时，先插入主表、再插入从表</p>
<p>​      删除数据时，先删除从表、再删除主表</p>
<p>修改表时添加约束</p>
<p>添加列级约束</p>
<p>alter table 表名 modify column 字段名 字段类型 新约束</p>
<p>添加表级约束</p>
<p>alter table 表名 add 【constraint 约束名】 约束类型（字段名）【外键的引用】</p>
<pre class="line-numbers language-sql" data-language="sql"><code class="language-sql"><span class="token keyword">alter</span> <span class="token keyword">table</span> stuinfo <span class="token keyword">modify</span> <span class="token keyword">column</span> stuname <span class="token keyword">varchar</span><span class="token punctuation">(</span><span class="token number">20</span><span class="token punctuation">)</span> <span class="token operator">not</span> <span class="token boolean">null</span><span class="token punctuation">;</span>
<span class="token keyword">alter</span> <span class="token keyword">table</span> stuinfo <span class="token keyword">modify</span> <span class="token keyword">column</span> age <span class="token keyword">int</span> <span class="token keyword">default</span> <span class="token number">18</span><span class="token punctuation">;</span>
<span class="token keyword">alter</span> <span class="token keyword">table</span> stuinfo <span class="token keyword">modify</span> <span class="token keyword">column</span> id <span class="token keyword">Int</span> <span class="token keyword">primary</span> <span class="token keyword">key</span><span class="token punctuation">;</span>
<span class="token keyword">alter</span> <span class="token keyword">table</span> stuinfo <span class="token keyword">add</span> <span class="token keyword">primary</span> <span class="token keyword">key</span><span class="token punctuation">(</span>id<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">alter</span> <span class="token keyword">table</span> stuinfo <span class="token keyword">modify</span> <span class="token keyword">column</span> seat <span class="token keyword">Int</span> <span class="token keyword">unique</span><span class="token punctuation">;</span>
<span class="token keyword">alter</span> <span class="token keyword">table</span> stuinfo <span class="token keyword">add</span> <span class="token keyword">unique</span><span class="token punctuation">(</span>seat<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">alter</span> <span class="token keyword">table</span> stuinfo <span class="token keyword">modify</span> <span class="token keyword">column</span> id <span class="token keyword">Int</span> <span class="token keyword">primary</span> <span class="token keyword">key</span><span class="token punctuation">;</span>
<span class="token keyword">alter</span> <span class="token keyword">table</span> stuinfo <span class="token keyword">add</span> <span class="token keyword">constraint</span> fk <span class="token keyword">foreign</span> <span class="token keyword">key</span><span class="token punctuation">(</span>majorid<span class="token punctuation">)</span> <span class="token keyword">references</span> major<span class="token punctuation">(</span>id<span class="token punctuation">)</span><span class="token punctuation">;</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>

<p>删除表时删除约束</p>
<p>后面约束类型不写即可</p>
<pre class="line-numbers language-sql" data-language="sql"><code class="language-sql"><span class="token keyword">alter</span> <span class="token keyword">table</span> stuinfo <span class="token keyword">modify</span> <span class="token keyword">column</span> stuname <span class="token keyword">varchar</span><span class="token punctuation">(</span><span class="token number">20</span><span class="token punctuation">)</span> <span class="token boolean">null</span><span class="token punctuation">;</span>
<span class="token keyword">alter</span> <span class="token keyword">table</span> stuinfo <span class="token keyword">modify</span> <span class="token keyword">column</span> age <span class="token keyword">int</span><span class="token punctuation">;</span>
<span class="token keyword">alter</span> <span class="token keyword">table</span> stuinfo <span class="token keyword">drop</span> <span class="token keyword">primary</span> <span class="token keyword">key</span><span class="token punctuation">;</span>
<span class="token comment">#删除唯一</span>
<span class="token keyword">alter</span> <span class="token keyword">table</span> stuinfo <span class="token keyword">drop</span> <span class="token keyword">index</span> seat<span class="token punctuation">;</span>
<span class="token keyword">alter</span> <span class="token keyword">table</span> stuinfo <span class="token keyword">drop</span> <span class="token keyword">foreign</span> <span class="token keyword">key</span> majorid<span class="token punctuation">;</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>



<h2 id="标识列"><a href="#标识列" class="headerlink" title="标识列"></a>标识列</h2><p>又称为自增长列<br>可以不用手动的插入值，<br>系统提供默认的序列值</p>
<p>标识列可以key（主键、唯一、外键或自定义key）搭配</p>
<p>一个表至多可以有一个标识列</p>
<p>标识列的类型只能是数值型</p>
<p>创建表时设置标识列</p>
<pre class="line-numbers language-sql" data-language="sql"><code class="language-sql"><span class="token keyword">create</span> <span class="token keyword">table</span> <span class="token keyword">if</span> <span class="token operator">not</span> <span class="token keyword">exists</span> tab_identity<span class="token punctuation">(</span>
	id <span class="token keyword">int</span> <span class="token keyword">primary</span> <span class="token keyword">key</span> <span class="token keyword">auto_increment</span><span class="token punctuation">;</span>
  name <span class="token keyword">varchar</span><span class="token punctuation">(</span><span class="token number">20</span><span class="token punctuation">)</span>
<span class="token punctuation">)</span>
<span class="token comment">#展示自增步长</span>
<span class="token keyword">show</span> variables <span class="token operator">like</span> <span class="token string">'%auto_increment'</span><span class="token punctuation">;</span>
<span class="token comment">#设置自增步长</span>
<span class="token keyword">set</span> auto_increment_increment<span class="token operator">=</span><span class="token number">3</span><span class="token punctuation">;</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>

<p>修改表时设置标识列</p>
<pre class="line-numbers language-sql" data-language="sql"><code class="language-sql"><span class="token keyword">alter</span> <span class="token keyword">table</span> tab_identity <span class="token keyword">modify</span> <span class="token keyword">column</span> id <span class="token keyword">int</span> <span class="token keyword">primary</span> <span class="token keyword">key</span> <span class="token keyword">auto_increment</span><span class="token punctuation">;</span>
<span class="token keyword">alter</span> <span class="token keyword">table</span> tab_identity <span class="token keyword">modify</span> <span class="token keyword">column</span> id <span class="token keyword">int</span><span class="token punctuation">;</span><span class="token comment">#删除标识列</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span></span></code></pre>


                
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